Known open-end rotor spinning machines are composed of a plurality of side-by-side arranged spinning units along which such a device is adapted to travel and to remedy thread breakages by effecting new yarn spinning-in. For the reliable operation of this device it is inevitable that it must be capable of perfectly introducing the yarn to be spun-in into the take-off tube.
In view of some inaccuracies in the machine manufacture, which are not economically avoidable, and of problems of precisely arresting the travelling unit opposite the work station, the precise location of the yarn introducting device onto the mouth of take-off tube is very troublesome. According to the German Published Patent Application (DE-OS) No. 2,361,787, this problem has been solved by the take-off or spinning-in tube being mounted in the spinning unit resiliently and centered by being engaged by said yarn end introducing device.
A disadvantage of this known device is that such a resiliently arranged take-off tube has to be provided at each of the spinning units and, since the tube is movable in necessary gaps to enable this motion, these gaps get choked with fibrous dust which may cause a tube malfunction, or even make the correct introduction of yarn up into the spinning rotor impossible.
Another device for automatic introduction of yarn into the outlet tube of spinning unit has been described in the German Published Patent Application (DE-OS) No. 2,711,163, wherein the precise positioning and fixation thereof relative to the spinning unit is effected e.g., by a spherical head disposed on the spinning unit, in cooperation with a corresponding wedge-like guide on the travelling unit, or by a conical pin on the spinning unit, and a ring-formed element on a defining rod of the travelling unit. Such a positioning device is designed for defining the position of the entire travelling unit relative to each of the spinning units. This German application also discloses another embodiment of the device for precisely introducing yarn into the outlet tube of the spinning unit wherein the spinning-in head is provided with a holder carrying a centering guide. After the spinning-in head has been brought, together with the guide, to the spinning unit, the centering guide will engage a centering surface provided in the spinning unit. In this way, the spinning-in head together with the yarn end is caused to assume the position above the outlet tube. The centering hole surface has a conical inlet so as to compensate for some inaccuracies while positioning the spinning-in head together with the centering guide.
A drawback of the above-described device is that such a positioning requires the entire mass of the spinning-in unit to be displaced whereby the positioning means get worn within a relatively short time. Another shortcoming is that it is necessary to sporadically adjust the positioning means in order to attain the exact reproduction of the spinning-in unit position above the outlet tube. For this reason, the centering hole surfaces are provided in a bar which is adjustably arranged on the spinning unit. In general, the device is relatively complicated and, apart from this, the bar may get unlocked due to machine vibrations whereby the precise location of the spinning-in head above the outlet tube is impaired.
A further disadvantage of the known device results from the swing motion of the lever supporting the spinning-in head. Even though the spinning-in head is resiliently mountd for a versatile motion relative to the take-off tube of the spinning unit, it cannot be avoided that, if the head is positioned askew at the end of said tube, gaps arise between the head and the tube and, apart from this, the yarn introducing element may get jammed at the end of the tube so that a difficult removal thereof may even cause malfunctions of the automatic travelling service unit.